1. Field of the Invention
The present invention relates generally to pneumatic tools, e.g. pneumatic wrench, and more particularly, to an impact device of a pneumatic tool.
2. Description of the Related Art
A pneumatic wrench primarily comprises a pneumatic motor, a shaft rotationally driven by the pneumatic motor, and a socket disposed at an end of the shaft. The socket is adapted to be sleeved onto a nut or the head of a screw and tighten or loosen the nut or screw when rotating along with the shaft.
Some pneumatic wrenches further comprise an impact mechanism. When the nut or screw is tightened to a certain extent that the rotational torque outputted by the pneumatic motor is no longer capable of driving the shaft to rotate, the impact mechanism can be driven to impact the shaft and thereby instantly increase the rotational torque of the shaft. In this way, the shaft can be driven to rotate at the moment of being impacted and therefore drive the socket to further tighten the nut or screw which is initially tightened, or loosen the nut or screw which is firmly tightened.
Specifically speaking, a conventional impact device 10 of a pneumatic tool, which is shown in FIGS. 1-2, comprises a shaft 11 as aforementioned, an impact cylinder 13 sleeved onto the shaft 11 and provided with two through grooves 12, an outer cylinder 15 sleeved onto the impact cylinder 13 and provided with two recesses 14, and two impact pins 16 respectively located in the through grooves 12 and movable into the recesses 14, respectively. The impact cylinder 13 is adapted to be rotationally driven by a pneumatic motor (not shown) so that the whole impact device 10 is driven to rotate. When the shaft 11 is unrotatable along with the impact cylinder 13, the impact pins 16 can be driven by the impact cylinder 13 and the outer cylinder 15 to impact the concave surfaces 17 of the shaft 11 intermittently so that the shaft 11 can be driven to rotate at the moment of being impacted.
In the aforesaid operating process of the impact device 10, the impact cylinder 13, the outer cylinder 15 and the shaft 11 are coaxial with each other all along, and one of the impact pins 16 is temporarily wedged between the impact cylinder 13 and the outer cylinder 15 as a result of the motion of the impact pins 16 going in and out of the recesses 14, so that the wedged impact pin 16 can impact the shaft 11 intermittently. Such impact device 10 can output sufficient torque; however, the impact device 10 has a relatively shorter lifetime resulted from frequent friction between the elements thereof and large impact forces.